This invention relates to the testing of wire, particularly to the testing of the conductive properties of a wire, and more particularly to a detector assembly for testing wire inhomogeneity to determine possible defects in the wire.
Various applications establish a need for determining the electrical properties of wire prior to use of the wire. For example, superconducting magnets typically require thousands of meters of superconducting wire. All too frequently, the superconductor is flawed, and there has been no convenient method for determining where the defects, if any, occur.
The operation of building a coil from conductive wire, for example, is extremely time-consuming and expensive. Furthermore, construction techniques for many superconducting magnets prevent replacement of wire after the coil has been completed. For this reason, every effort must be made to find any defects in the wire before assembling the coil. Traditional testing methods examine small segments of wire from the ends of the roll, but do not inspect the overall conductor quality. Occlusions, losses of superconducting filaments, or changes in cross section of the wire may be undetected and, thus, prevent the magnet's proper performance.
Various types of apparatus and methods have been developed for testing various properties of wire. For example, U. S. Pat. Nos. 2,960,652 issued Nov. 15, 1960 to W. P. Harris et al and 3,281,678 issued Oct. 25, 1966 to F. F. Cilyo are directed to determining the magnetic properties of the wire. U.S. Pat. No. 4,303,885 issued Dec. 1, 1981 to T. J. Davis relates to a digitally controlled eddy current test apparatus for detecting a flaw location in a wire. U.S. Pat. No. 3,283,245 issued Nov. 1, 1966 to R. A. Stauffer provides a testing method for the superconductivity wherein the superconductor is dipped in a cryogenic bath.
While these prior methods and apparatus have been effective for their intended purpose, a need has existed for a simple, but effective method for detecting inhomogeneity in a conductive wire over its entire length, especially superconducting wire to be utilized in magnets, etc.
Also, while eddy currents have been previously used to measure the quality of a copper surface, e. g., in radio frequency cavities, there is a need for a device that measures variations in eddy currents to reveal defects in wire, particularly superconducting wire, by gauging the proportion of conductive material in the wire in a given cross section.